The common practice in forming fibers of mineral material, such as glass fibers, is to pass the material in a molten state through the orifices of the peripheral wall of a centrifuge or spinner to create primary fibers. Thereafter, the primary fibers are further attenuated into secondary fibers of smaller diameter by the action of a flow of gases discharged downwardly from an external annular blower. Some fiber forming processes, such as the Supertel process, use a high velocity gaseous burner for the secondary attenuation of the mineral fibers. Other fiberizing processes, such as low energy processes, use blowers to turn the mineral fibers into a downwardly moving cylindrical veil.
All of these processes produce a downwardly moving substantially cylindrical veil of swirling gases and mineral fibers which are then collected on a forming chain in a forming hood. The diameter of the cylindrical veil will vary, depending on the fiberizing process employed, but in almost all cases it is necessary to widen the veil or distribute the veil in order to produce a mineral fiber product which is wider than the original veil of mineral fibers.
Numerous devices have been employed in the past to distribute the veil. These include mechanical impingement devices and many different kinds of gaseous jets. The aim of each of these distribution techniques is to produce a mineral fiber product having uniform fiber density across the width of the product. Also, it is important not to damage the fibers during the distribution process. Further, it is desirable to employ as little additional air or other gases as possible in the distribution process to avoid the burden of treating the additional gases for environmental purposes. A distribution method which increases the turbulence of the gaseous flows in the forming hood is undesirable because of fiber blow-back and the increased suction requirements beneath the forming chain.
The problem with most of the present veil distribution methods is that the veil is maintained as a relatively coherent, downwardly flowing, swirling flow of gases and mineral fibers, while it is lapped or distributed from side to side of the forming chain. Gaseous distribution devices, in combination with the suction of the fans beneath the forming chain, blast the fibers onto the forming chain, in the nature of a "slam dunk". There has long been a need for an improved system for distributing the fibers in the veil. Preferably, this system would transform the veil into a gently downwardly flowing incoherent mixture of fibers, in the nature of a snowstorm. The snowstorm distribution would avoid problems of blow-back, reduce the amount of air needed to be environmentally treated, and facilitate uniform density of the fibers across the width of the pack. The fibers would be merely floating downwardly, primarily under the influence of gravity, and could have their paths changed by suction in order to fill light spots in the pack because of the increased suction at those spots. Thus, there is a need for a distribution method and apparatus to turn the downwardly moving cylindrical veil of fibers into an incoherent gentle flow of fibers.